The purpose of this investigation is to elucidate the effects of general anesthesia and anesthetic techniques on cerebral metabolism, with particular emphasis being placed on the effects of carrier-mediated transfer of glucose between blood and brain. The study proposes to define the effects of general anesthesia on the in vivo kinetics of glucose transport in the dog brain. Measurements obtained during light N2O-O2 anesthesia will be compared with those obtained during anesthesia with Halothane, Morphine, or Enflurane. Subsequently, the effects of hypocarbia and hypoxia will be studied. Dogs will be anesthetized with N2O-O2 and pulmonary ventilation controlled in a manner which maintains end-tidal PCO2 constant at a normal level. Following the insertion of cannule into the carotid artery and sagittal sinus for blood sampling and drug injection, the inner directional transport of isotopically labeled glucose and fructose into the brain will be measured with the indicator dilution technique. Cerebral blood flow as well as cerebral oxygen and glucose consumption will be measured. Glucose transport will be correlated with cerebral metabolic rate, depth of anesthesia, and arterial PCO2 and PO2 levels.